The proposed research will attempt to design and construct a closed-loop control system for stabilizing antero-posterior postural sway at the ankle joint in paraplegic individuals standing by functional neuromuscular stimulation (FNS). The research is limited to the specific problem of quiet standing within narrow limits which are defined by contraints such as stabilization of the hip and torque available from electrically stimulated muscle. Mathematical models of upright posture will be simulated, and a closed-loop controller implemented on a digital computer. The system will iclude a computer controlled muscle stimulator for m. soleus and m. tibialis anterior. Goniometers, inclinometers and force shoes will be evaluated as sources of the regulated variable. The long-term objective is the realization of an implantable closed-loop electrical stimulation orthosis to restore leg function in upper motor neuron paralysis. In paraplegia resulting from spinal cord injury, the natural neural control system is damaged. Paraplegics must presently rely on knee-ankle-foot orthoses for standing and forward progression. The expectation that FNS can further improve the ability of paraplegics to stand and make biped forward progression is predicted on the assumption that upright stability and postural sway can be controlled by means of FNS.